1. Field of the Invention
The present invention relates to a permanent magnet and reluctance type rotating machine.
2. Description of the Related Art
FIG. 1 shows the schematic structure of a permanent magnet and reluctance type rotating machine (not prior art).
In FIG. 1, the permanent magnet and reluctance type rotating machine 101 comprises a stator 103 carried by a housing or the like and a rotor 105 rotatably arranged in the stator 103. The stator 103 consists of a stator core 107 and armature windings 109 wound around the stator core 107. In the rotor 105, four pairs of permanent magnets 113 are arranged crosswise in a rotor core 111. Magnetic poles 115 are defined by respective core portions in which the magnetic permanents 113 are arranged, while interpoles 119 are constituted by non-magnetic portions 117 between the permanent magnets 113.
FIG. 2 shows magnetic flux .phi. d due to the armature current, flowing along the directions of respective pole axes of the rotor core 111. In this state, since the magnetic paths are constituted by the core portion forming the poles 115, the flux is easy to flow because of an extremely small magnetic reluctance.
FIG. 3 shows another magnetic flux .phi. e due to the armature current, flowing along the directions of respective radial axes passing through respective circumferential centers of the interpoles 119. Although the magnetic flux .phi. e of the interpoles 119 does build the magnetic paths crossing the permanent magnets 113 interposing the interpoles 119, the flux due to the armature current is decreased under the high reluctance action of the permanent magnets 113 because of their relative permeability of approx. 1.
The permanent magnets 113 on both sides of each interpole 119 are magnetized in the directions substantially perpendicular to the pole axes. Therefore, as shown in FIG. 4, the flux generated from each permanent magnet 113 partially circulates in the following order: one pole of the permanent magnet 113, a magnetic portion 121 in the vicinity of the periphery of the core 111, the pole 115 and the opposite pole of the magnet 113, thereby to form a magnetic circuit .phi. ma. Further, a part of flux from each permanent magnet 6 also flows into the stator 107 through the gap between the rotor 105 and the stator 107 and subsequently passes through the pole 115 of the rotor 105, the neighboring permanent magnet 6 and the originating permanent magnet 113 in order, thereby to form another magnetic circuit .phi. mb.
Returning to FIG. 3, the interlinkage flux of the permanent magnets 113 distributes in the opposite direction to the magnetic flux .phi. e (by the armature current) flowing along the center axes of the interpoles 119 to repel the magnetic flux .phi. e into their mutual negation. At the gap in the vicinity of each interpole 119, there is a reduction in gap flux density derived from the armature current due to the flux of the permanent magnets 113. Consequently, there is produced a great change in the gap flux density between the vicinity of each pole and that of each interpole. In other words, the change of gap flux density with respect to the rotational position of the rotor 105 becomes so large that the change of magnetic energy is increased. Further, under the loaded situation, the rotor 105 is subjected to great magnetic saturation by load currents owing to the presence of the magnetic portions 121 each forming a magnetic short circuit on the boundary between the pole 115 and the interpole 119. The magnetic flux of the magnets 113 distributed in the interpoles 119 is increased. Consequently, there is produced a great unevenness in the distribution of gap flux density by both magnetic reluctance and flux of the permanent magnets 113 and therefore, the magnetic energy is remarkably changed to produce a great output.
Next, we describe the adjusting range of terminal voltage in order to accomplish the operation of the rotating machine at a wide range of variable speeds. Since the permanent magnets 113 exist in only a part of each interpole 119, the rotating machine has a narrow surface area of the permanent magnets 113 in comparison with that of the general rotating machine where the permanent magnets are arranged in the whole circumference of the rotor, also exhibiting a small interlinkage flux due to the permanent magnets 113.
Furthermore, under condition that the machine is unexcited, a considerable quantity of the permanent magnets' flux flows the magnetic portions 121 to become the leakage flux in the rotor core 111. Accordingly, since it is possible to reduce an induced voltage remarkably in this condition, the core loss at the machine's unexciting is reduced. Additionally, when the windings 109 malfunction in a short circuit, the over-current is reduced.
When the rotating machine is loaded, the terminal voltage is induced owing to the addition of interlinkage flux by the armature current (i.e. both exciting current and torque current of the reluctance rotating machine) into the interlinkage flux by the permanent magnets 113.
In the general permanent magnet type rotating machine, it is impossible to adjust the terminal voltage since a great deal of terminal voltage is occupied with the interlinkage flux of the permanent magnets 113. While, in the permanent magnet-reluctance type rotating machine 101, it is possible to adjust the terminal voltage in a wide range by controlling the component of exciting current because of small interlinkage flux of the permanent magnets 113. In other words, as the component of exciting current can be adjusted so as to attain the terminal voltage less than a voltage of the power source voltage corresponding to the velocity, the rotating machine is capable of driving at a wide range of variable speeds (from its base speed) to by a constant voltage.
Furthermore, as the voltage is not restricted by field-weakening under the forced control, there is no possibility of the occurrence of over-voltage even if the control is not effected at the time of the machine's rotating at high speed.
Additionally, since a part of flux from each permanent magnet 113, that is, flux .phi. ma leaks out into the short circuit of the magnetic portion 121, it is possible to reduce the diamagnetic field in the permanent magnets 113. Thus, since the permanent magnet's operational point is raised on its demagnetizing curve representing the B(magnetic flux density)--H(field intensity) characteristics, that is, the permeance coefficient becomes large, the demagnetizing-proof characteristics against temperature and armature reaction is progressed. Additionally, as the permanent magnets 113 are embedded in the rotor core 111, it will be expected that the rotating machine has a merit to prevent the permanent magnets 113 from scattering due to the rotation of the rotor 105.
On the contrary, since respective core portions around holes 123 for the permanent magnets 113, especially, radial outside portions of the interpoles 119 are formed as thin as possible in view of reducing the flux leakage from the magnets 113, it is unexpectedly difficult to cope with centrifugal force of the permanent magnets 113 in the above-mentioned rotating machine. Particularly, in case of the application for a high-speed rotating machine, there may be caused various problems of the scattering of the permanent magnets 113, the breakage of the rotor 105, etc.